WO2000048833A1

WO2000048833A1 - Wettable soft polyolefin fibers and fabrics

Info

Publication number: WO2000048833A1
Application number: PCT/US2000/004099
Authority: WO
Inventors: Valeria Griep Erdos; Carlos Viramontes; Rocío GUAJARDO
Original assignee: Polymer Group, Inc.
Priority date: 1999-02-19
Filing date: 2000-02-17
Publication date: 2000-08-24
Also published as: US20010010989A1; AU3598900A; US20010010990A1; US6239047B1

Abstract

A wettable fiber or filament comprises a melt additive to a thermoplastic polyolefin such as polypropylene. The melt additive is a polyethylene oleiyl ether having the formula: R-O-{-CH2-CH2-O}x-CH2-CH2-O-H where x is an integer from 1-15, and R=CH3-(CH2)7-CH=CH-(CH)8-I-. When the foregoing ether is added to a melt of polypropylene at levels of 2-15 % by weight prior to the extrusion of the fibers or filaments, and the fibers or filaments are formed into fabrics, the fibers, filaments, or fabrics will exhibit permanent wettability, as well as excellent drape and softness. Such fabrics are useful, for example, as the skin contacting inner lining fabric of sanitary articles such as diapers, feminine hygiene products and the like.

Description

WETTABLE SOFT POLYOLEFIN FIBERS AND FABRICS

Background of the Invention

This invention relates to a melt-extrudable thermoplastic polyolefin-based

composition which when extruded into films, fibers, nonwoven fabrics or composites,

results in a material or nonwoven fabric which exhibits durable wettability.

Polyolefins, especially polypropylene, are used in large quantities to make

nonwoven fabrics and films. Polyolefin nonwoven fabrics, such as carded webs,

spunbond, meltblown or composites thereof, are preferred as components in sanitary

articles, such as single use diapers, feminine hygiene products and incontinence care

products. The recognized benefits of polyolefin based, especially polypropylene,

fabrics include the relatively low raw material cost, ease of manufacturing, desirable

strength to basis weight ratio and softness.

Sanitary articles generally contain an absorbent core component of materials

capable of absorbing several times their weight in liquids. Usually the article includes

at least one outer covering or lining which contacts the user's skin on one side of the

core and the an exterior layer contacting the environment on the other side of the core.

Softness and liquid permeability are required of fabrics used for the inner linings. The

liquid permeability should take the form of allowing liquid to pass through the fabric

and into the inner absorbent core, while not actually absorbing fluids in the process.

An additional desired feature is for the inner lining, i.e. the cover sheet for the

absorbent core, to remain fluid permeable even after extended wear and repeated insults

of fluid, such as routinely occurs with infant diapers in situ. Another highly desired, but difficult to provide, feature of inner lining fabrics is that they resist having liquids

collected in the absorbent core bleed back through to the user's skin when pressure is

applied - such as an infant sitting in a wet diaper.

Nonwoven fabrics and composites made of cellulosic materials pass and absorb

liquids even after repeated insults, but they do not routinely resist the flow back of the

retained fluids under pressure. Thermoplastic fibers, such as polyesters and polyolefins

have already been described as being preferred for these end uses for economic,

aesthetic and strength reasons. However, polypropylene is, by its nature, hydrophobic.

When spun into fibers or filaments which are used to form a fabric, the resulting fabric

is also hydrophobic or non-wettable. Thus, the fabric must be specially treated or

altered in some way to render the fabric wettable, that is, able to allow the passage or

transfer of fluids, if the fabric is to be suitable for use as an inner lining fabric for a

sanitary article.

For purposes of clarification, it should be noted that absorption indicates that

the material actually swells with added water. In contrast, wettability, such as used

herein, denotes a change in surface tension that permits a layer of water to form on the

surface of a solid, such as a fiber, for the purpose of facilitating the movement of the

liquid flow past or through the wettable material.

It is known in the industry that certain surfactants, such as Triton X-100 from

Rohm and Haas, can be applied as an aqueous solution or suspension to the surface of

hydrophobic fibers, filaments or nonwoven fabrics with the resulting effect of

rendering the fibers, filaments or fabrics wettable, although not absorbent. These topical treatments can be applied by any means familiar to one skilled in the art, such

as foaming, spraying, dip-and-squeeze or gravure roll. In almost every case, some sort

of heating step is required to remove residual water or solvents used to prepare the

surfactant solution or suspension. This step adds significantly to the manufacturing

costs and complexity. Further, thermoplastics are altered by exposure to heat and

careful monitoring of the heating process is required to ensure that fabric properties are

not adversely affected. Further, the surfactants are not strongly chemically bonded to

the fiber or filament surfaces, such topical treatments are not durable. They tend to

wash off during repeated fluid insults or rub off during use.

In an effort to correct this deficiency, corona discharge treatments have been

used to alter the electrochemical potential of the surfaces of fibers or filaments. The

effect is to render surfaces more reactive with the result that hydrophobic surfaces

become more wettable. However, these electrical potential changes are also not

permanent, being particularly subject to environmental effects, such as storage in moist

environments.

An additional advancement is the use of surface chemical treatments where the

surfactants are covalently bonded to the polymer.

Another approach is the incorporation of chemical agents in the thermoplastic

polymer before it is extruded into fibers, filaments or nonwoven fabrics. Agents, such

as siloxanes, have been proposed for this purpose. Here, the object is to impart a

durable change in the wettability of the fibers or filaments. The performance model

theory states that the melt additives become dispersed in the molten polymer and are bound in the matrix when the polymer cools during fiber or filament quenching. Over

time, or due to the effects of further processing, the additive rises to the surface of the

fibers or filaments, a phenomenon called blooming, imparting durable wettability.

Fatty acid esters have been used as fabric softener compounds, such as

described in U.S. patent no. 5,593,614. The melt addition of a di-fatty ester to polyolefins is described in U.S. patent no. 5,439,734 to Kimberly-Clark. The melt

addition of this di-acid ester was described as imparting wettability durable up to three

fluid insults.

Polyethylene glycols esters (PEG esters) have been recognized as useful in the

preparation of hydrogels and wettable membranes, directed towards wound care, as

described in U.S. patent nos. 5,700,286 and 5,698,074. PEG esters have also been

used to topically treat hydrophobic fibers, as described in U.S. patent no. 4,073,993.

Summary of the Invention

In accordance with the present invention , a melt additive to a thermoplastic

polyolefin such as polypropylene is provided in which the additive is a polyethylene

oleiyl ether having the formula:

R-O-{-CH₂ - CH₂ -O}_x -CH₂ -CH₂ -O-H

where :

x is an integer from 1-15, and

R = CH₃ -(-CH₂)₇ -CH=CH-(-CH )₈ ~. When the foregoing ether is added to a melt of polypropylene at levels of two to

fifteen percent by weight prior to the extrusion of the fibers or filaments, and the fibers

or filaments are formed into fabrics, the fibers, filaments or fabrics will exhibit

permanent wettability, as well as an unanticipated improvement in softness and drape.

It has been demonstrated by Transmission Electron Microscopy that the PEG oleiyl

ether is distributed throughout the cross-section of the fibers or filaments with a

concentration at the surface skin of the formed fibers or filaments.

The wettable fabrics produced from the fibers or filaments of this invention are

particularly useful, for example, as the skin contacting inner lining fabric of sanitary

articles, particularly single use diapers, feminine hygiene products or incontinence care

products. The fabrics produced may also have utility in wet and dry wipes, filter

media, battery separators and the like.

Detailed Description of the Invention

This invention is applicable to processes in which a thermoplastic polymer,

especially a polyolefin such as polyethylene or polypropylene, is melted and extruded

to form fibers or filaments. In accordance with known technology such as continuous

filament spinning for yarn or staple fiber, and nonwoven processes such as spunbond

production and meltblown production, the fibers or filaments are formed by extrusion

of the molten polymer through small orifices. In general, the fibers or filaments thus

formed are then drawn or elongated to induce molecular orientation and affect

crystallinity, resulting in a reduction in diameter and an improvement in physical properties. In nonwoven processes such as spunbonding and meltblowing the fibers or

filaments are directly deposited onto a foraminous surface, such as a moving flat

conveyor and are at least partially consolidated by any of a variety of means including,

but not limited to, thermal, mechanical or chemical methods of bonding. It is known

to those skilled in the art to combine processes or the fabrics from processes to produce composite fabrics which possess certain desirable characteristics. Examples of this are

combining spunbond and meltblown to produce a laminate fabric that is best know as

SMS, meant to represent two outer layers of spunbond fabric and an inner layer of

meltblown fabric. Additionally either or both of these processes may be combined in

any arrangement with a staple fiber carding process or bonded fabrics resulting from a

nonwoven staple fiber carding process. In such described laminate fabrics, the layers

are generally at least partially consolidated by one of the means listed above. The

invention is also applicable to melt extruded bicomponent fibers, wherein one of the

components is a polyolefin.

Spunbond filament sizes most useful for wettable fabrics of the anticipated type

are 1.0 - 3.2 denier. Meltblown fibers typically have a fiber diameter of less than 15

microns and most typically for the anticipated applications are fiber diameters less than

5 microns, ranging down to the submicron level. Webs in a composite construction

may be processed in a wide variety of basis weights.

As described, thermoplastic polypropylene fibers, which are typically extruded

at temperatures in the range of 210° - 240°C, are inherently hydrophobic in that they

are essentially non-porous and consist of continuous molecular chains incapable of attracting or binding to water molecules. As a result, untreated polypropylene fabrics,

even while having an open pore structure, tend to resist the flow of liquids such as

water or urine through the fabric, or from one surface to the other.

In accordance with the present invention, a PEG ether, specifically a PEG oleiyl

ether is incorporated into a thermoplastic polyolefin, such as polypropylene, in the melt and is extruded with the polyolefin into the form of fibers and filaments which are then

quenched, attenuated and formed into fabrics, either in a subsequent or concomitant

processing step. The general formula for the preferred compound is:

R-O-{-CH₂ - CH₂ -O}_x -CH₂ -CH₂ -O-H

where :

x is an integer from 1-15, and

R = CH₃ -(-CHj), -CH=CH-(-CH ), -.

The PEG oleiyl ether is characterized by IR bands at 3436 cm^"1 (glycol ether)

and near 1123 cm^'1 (ether linkage).

The PEG ether may be compounded with the polymer pellets which are to be

melt extruded. To improve the processing, the compound may be preformulated or

compounded into a low MFR polypropylene which may also contain a small amount of

an inorganic powder, such as talc, and an antioxidant. The total amount of PEG ether

added is 2 to 15% on a weight by neat polypropylene weight basis. For many

applications, the most preferred range is from about 3 to about 7 percent by weight.

Addition levels below the indicated minimum level do not produce the desired degree of wettability in the fibers, filaments or fabrics. Addition levels above the indicated maximums do not provide significant additional performance benefits. One suitable

ether compound, identified by the designation Techmer S-215834E25, is available from

Techmer PM.

Nonwoven fabrics made from internally treated polypropylene exhibit properties

which are greatly superior to other internal additives or topical treatments known in the

prior art. The PEG ether compound is observed by Transmission Electron

photomicrographs to be distributed throughout the fiber cross section, while showing a

tendency to migrate toward the surface skin of the fibers or filaments. This results in

the observed improved wettability of naturally hydrophobic fibers, filaments or fabrics,

and also contributes to the durability of that modification, such that the fibers,

filaments and fabrics do not lose their wettability upon aging or handling. Further, the

improved wettability is stable to repeated fluid insults, up to seven times, without a loss

of performance, even over extended time periods. Finally, there is an unexpected

aesthetic benefit as the fabrics produced from the fibers or filaments of this invention

are considerably softer than untreated fabrics. This feature can be measured as a

significant change in the coefficient of static or dynamic friction.

While the present invention has been described especially in connection with

nonwoven polyolefin fabrics, particularly polypropylene fabrics, it will be apparent to

those skilled in the art that the internally treated fibers or filaments may also be formed

into threads or yarns for weaving or knitting in conventional textile processes. Also, irrespective of the desired property of wettability, the melt additive of the present invention may be employed where fabric sofmess and drape are the most important or controlling criteria.

In connection with nonwoven fabrics, it will be appreciated by those skilled in

the art that many of the properties of nonwoven fabrics are influenced by factors not

directly relevant to the present invention. These factors include, for example, basis

weight, fiber diameter, degree of and type of bonding of the fibers and the synergistic

effects and influence of composite structures, such as the already described SMS

structures.

It will also be appreciate by those skilled in the art that the performance benefits

associated with the practice of this invention are not limited to single component fibers.

Polyolefin bicomponent fibers, particularly side-by-side or sheath-core fibers of polypropylene and polyethylene would be expected to demonstrate the same practical

benefits as single component fibers of either type. It would be particularly efficacious

to include the melt additive only in the polyethylene component as that softer polymer

could be expected to promote more efficient blooming of the PEG ether to the surface

of that component of the fiber or filament.

In addition, it is often desirable to impart wettability and softness to melt

extruded polyolefin films. Such films, in perforated form, are widely used as cover

sheets for sanitary articles.

In one preferred embodiment for cover stock for sanitary articles, improvements in wetback properties can be improved by the use of two or more layers of fabric bonded together. Examples include two spunbond layers or an SMS fabric in which

the meltblown layer is devoid of the PEG ether.

Claims

Claims:

1. A soft, durably wettable polyolefin fiber or filament, said fiber or filament

comprising a melt blend of from about 2 to 15 percent by weight of a polyethylene

glycol oleiyl ether and the remainder as a thermoplastic polyolefin.

2. The fiber of Claim 1 wherein said polyethylene glycol oleiyl ether is represented

by the formula:

R-O-{-CH₂ - CH₂ -O}_x -CH₂ -CH₂ -O-H where :

x is an integer from 1-15, and

R = CH₃ -(-CH₂)₇ -CH=CH-(-CH )₈ ~.

3. A soft, durably wettable nonwoven fabric, said fabric comprising bonded fibers

or filaments of a thermoplastic polyolefin, said fibers or filaments comprising a melt

additive polyethylene glycol oleiyl ether in an amount from about 2 to 15 percent by

weight and about 98 to 85 percent of the thermoplastic polyolefin, said ether providing

softness and surface wettability to said fabric.

4. A nonwoven fabric of Claim 3 where the thermoplastic polyolefin is

polypropylene.

5. A nonwoven fabric of Claim 3 where the thermoplastic polyolefin is

polyethylene.

6. A nonwoven fabric of Claim 3 comprised of bicomponent fibers comprising a

polyolefin component, and wherein the polyethylene glycol oleiyl ether is an additive in the polyolefin component.

7. A fabric of Claim 3 wherein said polyethylene glycol oleiyl ether is present in the

amount from about 3 to about 7 percent.

8. A method for imparting softness and permanent wettability to a polyolefin fiber,

filament and fabric made therefrom, said method comprising the steps of melt

extruding a mixture of a thermoplastic polyolefin and from about 2 to about 15 percent

of a polyethylene glycol oleiyl ether into a plurality of fibers and cooling the fibers.

9. The method of Claim 5 wherein said fibers are drawn into a plurality of

continuous filaments, a web is formed from said filaments and the filaments are at least

partially bonded to form a coherent sheet.

10. A method of Claim 5 where the thermoplastic polyolefin is polypropylene.

11. A method of Claim 5 where the thermoplastic polyolefin is polyethylene.

12. A method of Claim 5 where the fibers or filaments are a bicomponent fiber or

filament comprising a polyolefin.

13. A melt extruded polyolefin product in the form of fibers, filaments and fims,

said product comprising a melt blend of from about 2 to 15 percent by weight of a polyethylene glycol oleiyl ether and the remainder as a thermoplastic polyolefin.

14. The melt extruded polyolefin product of Claim 13 wherein said product is a

film.

15. The product of Claim 14 in which the film is apertured.

16. The product of Claim 15 wherein the product comprises two layers of spunbond

fabrics.

17. The product of Claim 16 wherein the product additionally comprises an inner

meltblown layer.

18. The product of Claim 17 wherein the meltblown layer is devoid of said ether.